For many years it has been tried to develop methods for rapid chemical analysis of molten metal, especially in the steel industry. The driving force in this work has been the substantial economical savings which are possible by faster smelting- and refining processes and the possibility for an improved process control, thereby obtaining metals and metal alloys having a chemical composition within specifications.
The main type of rapid chemical analysis in the metal industry, especially in the steel industry, is being done by arc discharge optical emission spectrometry and x-ray fluorescence analysis on solid test specimens. The time interval from drawing a sample until a final analysis is obtained is normally in the range from 2 to 10 minutes.
A number of methods for direct analysis of molten metals have been proposed. Most of these methods are, however, difficult to use under operating conditions in metal smelting plants.
A group of proposed methods for direct analysis of molten metals is based on optical emission spectrometry. Thus use of arc discharge optical emission spectrometry on molten metal is described by Eizo Nonomura et al. in Transactions ISIJ, Vol. 25, 1985. Tests have shown that it is possible to use this principle for analysis of molten metal under controlled conditions, but that it is difficult to use under operating condition in smelting plants.
Laser-induced optical emission spectrometry for direct analysis of molten metals is described by Kouzou Tsunoyama et al. in Transactions ISIJ Vol. 25, 1985. By this method a laser is used for discharging the specimen, Masao Saeki, Proceeding from CETAS meeting in Luxemburg May 12.-14., 1987 has proposed to analyse the manganese content in a steel melt in a steel converter by using oxygen induced optical emission spectrometry.
Another method for direct analysis of molten metal comprises production of a volatized test specimen and transport of the specimen through a piping system to an IPC torch (Inductively coupled Plasma), wherein the test specimens is analysed. The test specimen can be obtained by a number of techniques, such as inserting a probe down into the metal bath and bubbling an inert gas through the bath, by reacting an oxidizing gas such as HCl, O.sub.2 or Cl.sub.2 with the bath, or by discharging an electric arc against the surface of the metal bath. Except for laboratory--and pilot plant tests, the method has not found any use. The method is described by G. Jecko and A. Golloch in Proceeding from CETAS meeting in Luxemburg May 12.-14., 1987.
Finally, I. A. Majorov et al, Spectrochimica Acta, Vol. 36, No. 12, 1981, page 1223-1231, has shown that atomic absorption spectrometry (AAS) can be used for continuous analysis of a metal melt during vacuum refining. In this method a light beam is passed through the gas phase above the molten metal bath in parallel with the surface of the molten metal bath.
For some elements and gases it is possible to analyse the content of the elements in a molten metal by using electrochemical sensors. Such electrochemical sensors can, however, only be used for analysing one element at a time and a sensor can only be used once. Electrochemical sensors are widely used for analysing oxygen content in steel melts and there are also described electrochemical sensors for analysing hydrogen, silicon, aluminium and calcium in molten metals.